The present invention relates generally to virtual image display systems, and more particularly, to an ultra-compact, wide field of view, virtual image display system.
Virtual image displays (VID), such as head-up displays (HUD) and helmet-mounted displays (HMD), are generally comprised of a combiner and a relay group. The prior art relating to head-up displays is generally classified into two categories: a display having (1) one combiner and an all-refractive relay group or, (2) one combiner and a convex reflective relay group. In case (1), the effects of the asymmetrical geometry of the combiner are undone by the refractive relay. Generally, the image quality is seriously compromised. In case (2), the generic telephoto optical form limits the usable field of view. These deficiencies are overcome by the present invention.
More particularly, relevant prior art relating to head-up displays and helmet mounted displays is discussed below. The drawbacks of these prior an displays are also summarized below.
A typical conventional head-up or helmet mounted display is disclosed in U.S. Pat. No. 3,940,204, entitled "Optical Display Systems Utilizing Holographic Lenses", issued to Withrington. This optical system includes three sub-modules: one holographic combiner, one relay group and one cathode my tube (CRT). The information displayed on the CRT is first relayed by a relay group to form an intermediate image and further relayed by the combiner to a comfortable position in front of a viewer. This optical design form has the following advantages: (1) The relay group allows the size of the CRT to be small. (2) The relay group enlarges the area of the overlay field. (3) The combiner relays the eye box (pupil) inside the relay group, so, therefore the size of the relay group is small.
However, the significant drawback of such an optical system is the large bending angle associated with the combiner. The aberration introduced by the combiner due to the bending of the line-of-sight often limits the image quality and the size of the optical system. To compensate and reduce the aberrations, three design steps have generally been taken: (1) applying tilt and decentration to optical elements of the relay group to provide for aberration compensation; (2) employing anamorphic optical elements such as prisms and cylindrical lenses for aberration balance; (3) reducing the bending angle of the combiner to minimize the aberration introduced by the combiner. Unfortunately, these techniques result in a smaller usable field of view and smaller field overlaying.
Other patents relating to virtual image display systems and related technologies are disclosed in U.S. Pat. No. 4,669,810, entitled "Display System", issued to Wood; U.S. Pat. No. 4,740,780, entitled "Head-Up Display For Automobile", issued to Brown et al.; U.S. Pat. No. 3,697,154, entitled "Optical Viewing System", issued to Johnson; U.S. Pat. No. 3,723,805, entitled "Distortion Correction System", issued to Scarpino et al.; U.S. Pat. No. 4,042,957, entitled "Display Systems", issued to Ellis; U.S. Pat. No. 3,784,742, entitled "Ground-Based Flight Simulating Apparatus", issued to Burnham et al.; U.S. Pat. No. 4,294,515, entitled "Virtual Image Display Apparatus", issued to Kaufman; U.S. Pat. No. 3,549,803, entitled "Virtual Image System For Training Simulator", issued to Bechtet al.; U.S. Pat. No. 4,973,139, entitled "Automotive Head-Up Display", issued to Weihrauch et al.; and European Patent Application No. 229,876, entitled "On-vehicle head up display device", by Yoshiyuki et al.